Re: [PATCH v4 3/5] fw_cfg: do DMA read operation

From: Gabriel L. Somlo
Date: Sun Nov 12 2017 - 07:52:49 EST

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On Tue, Oct 31, 2017 at 04:19:36PM +0100, Marc-André Lureau wrote:
> Modify fw_cfg_read_blob() to use DMA if the device supports it.
> Return errors, because the operation may fail.
>
> To avoid polling with unbound amount of time, the DMA operation is
> expected to complete within 200ms, or will return ETIME error.
>
> We may want to switch all the *buf addresses to use only kmalloc'ed
> buffers (instead of using stack/image addresses with dma=false).
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>

A couple of silly questions, inline, below.

Thanks,
--G

> ---
> drivers/firmware/qemu_fw_cfg.c | 154 ++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 137 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> index 1f3e8545dab7..8ce5e49b7c62 100644
> --- a/drivers/firmware/qemu_fw_cfg.c
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -33,6 +33,8 @@
> #include <linux/slab.h>
> #include <linux/io.h>
> #include <linux/ioport.h>
> +#include <linux/delay.h>
> +#include <linux/dma-mapping.h>
>
> MODULE_AUTHOR("Gabriel L. Somlo <somlo@xxxxxxx>");
> MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
> @@ -43,12 +45,26 @@ MODULE_LICENSE("GPL");
> #define FW_CFG_ID 0x01
> #define FW_CFG_FILE_DIR 0x19
>
> +#define FW_CFG_VERSION_DMA 0x02
> +#define FW_CFG_DMA_CTL_ERROR 0x01
> +#define FW_CFG_DMA_CTL_READ 0x02
> +#define FW_CFG_DMA_CTL_SKIP 0x04
> +#define FW_CFG_DMA_CTL_SELECT 0x08
> +#define FW_CFG_DMA_CTL_WRITE 0x10
> +#define FW_CFG_DMA_TIMEOUT 200 /* ms */
> +
> /* size in bytes of fw_cfg signature */
> #define FW_CFG_SIG_SIZE 4
>
> /* fw_cfg "file name" is up to 56 characters (including terminating nul) */
> #define FW_CFG_MAX_FILE_PATH 56
>
> +/* platform device for dma mapping */
> +static struct device *dev;
> +
> +/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
> +static u32 fw_cfg_rev;
> +
> /* fw_cfg file directory entry type */
> struct fw_cfg_file {
> u32 size;
> @@ -57,6 +73,12 @@ struct fw_cfg_file {
> char name[FW_CFG_MAX_FILE_PATH];
> };
>
> +struct fw_cfg_dma {
> + u32 control;
> + u32 length;
> + u64 address;
> +} __packed;
> +
> /* fw_cfg device i/o register addresses */
> static bool fw_cfg_is_mmio;
> static phys_addr_t fw_cfg_p_base;
> @@ -75,12 +97,93 @@ static inline u16 fw_cfg_sel_endianness(u16 key)
> return fw_cfg_is_mmio ? cpu_to_be16(key) : cpu_to_le16(key);
> }
>
> +static inline bool fw_cfg_dma_enabled(void)
> +{
> + return fw_cfg_rev & FW_CFG_VERSION_DMA && fw_cfg_reg_dma;
> +}
> +
> +static bool fw_cfg_wait_for_control(struct fw_cfg_dma *d, unsigned long timeout)
> +{
> + ktime_t start;
> + ktime_t stop;
> +
> + start = ktime_get();
> + stop = ktime_add(start, ms_to_ktime(timeout));
> +
> + do {
> + if ((be32_to_cpu(d->control) & ~FW_CFG_DMA_CTL_ERROR) == 0)
> + return true;
> +
> + usleep_range(50, 100);
> + } while (ktime_before(ktime_get(), stop));
> +
> + return false;
> +}
> +
> +static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control)
> +{
> + dma_addr_t dma_addr = 0;
> + struct fw_cfg_dma *d;
> + dma_addr_t dma;
> + ssize_t ret = length;
> + enum dma_data_direction dir =
> + (control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0);
> +
> + if (address && length) {
> + dma_addr = dma_map_single(dev, address, length, dir);
> + if (dma_mapping_error(NULL, dma_addr)) {
> + WARN(1, "%s: failed to map address\n", __func__);
> + return -EFAULT;
> + }
> + }
> +
> + d = kmalloc(sizeof(*d), GFP_KERNEL | GFP_DMA);
> + if (!d) {
> + ret = -ENOMEM;
> + goto end;
> + }
> +
> + dma = dma_map_single(dev, d, sizeof(*d), DMA_BIDIRECTIONAL);
> + if (dma_mapping_error(NULL, dma)) {
> + WARN(1, "%s: failed to map fw_cfg_dma\n", __func__);
> + ret = -EFAULT;
> + goto end;
> + }
> +
> + *d = (struct fw_cfg_dma) {
> + .address = cpu_to_be64(dma_addr),
> + .length = cpu_to_be32(length),
> + .control = cpu_to_be32(control)
> + };
> +
> + iowrite32be((u64)dma >> 32, fw_cfg_reg_dma);
> + iowrite32be(dma, fw_cfg_reg_dma + 4);
> +
> + if (!fw_cfg_wait_for_control(d, FW_CFG_DMA_TIMEOUT)) {
> + WARN(1, "%s: timeout", __func__);
> + ret = -ETIME;
> + } else if (be32_to_cpu(d->control) & FW_CFG_DMA_CTL_ERROR) {
> + ret = -EIO;
> + }
> +
> + dma_unmap_single(dev, dma, sizeof(*d), DMA_BIDIRECTIONAL);
> +
> +end:
> + kfree(d);
> + if (dma_addr)
> + dma_unmap_single(dev, dma_addr, length, dir);
> +
> + return ret;
> +}
> +
> /* read chunk of given fw_cfg blob (caller responsible for sanity-check) */
> -static inline void fw_cfg_read_blob(u16 key,
> - void *buf, loff_t pos, size_t count)
> +static ssize_t fw_cfg_read_blob(u16 key,
> + void *buf, loff_t pos, size_t count,
> + bool dma)
> {
> u32 glk = -1U;
> acpi_status status;
> + ssize_t ret = count;
>
> /* If we have ACPI, ensure mutual exclusion against any potential
> * device access by the firmware, e.g. via AML methods:
> @@ -90,17 +193,36 @@ static inline void fw_cfg_read_blob(u16 key,
> /* Should never get here */
> WARN(1, "fw_cfg_read_blob: Failed to lock ACPI!\n");
> memset(buf, 0, count);
> - return;
> + return -EBUSY;

Why EBUSY here (and not, e.g., EINVAL) ?

> }
>
> mutex_lock(&fw_cfg_dev_lock);
> - iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
> - while (pos-- > 0)
> - ioread8(fw_cfg_reg_data);
> - ioread8_rep(fw_cfg_reg_data, buf, count);
> + if (dma && fw_cfg_dma_enabled()) {
> + if (pos == 0) {
> + ret = fw_cfg_dma_transfer(buf, count, key << 16
> + | FW_CFG_DMA_CTL_SELECT
> + | FW_CFG_DMA_CTL_READ);
> + } else {
> + iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
> + ret = fw_cfg_dma_transfer(0, pos, FW_CFG_DMA_CTL_SKIP);

s/0/NULL/ ?

> + if (ret < 0)
> + goto end;
> + ret = fw_cfg_dma_transfer(buf, count,
> + FW_CFG_DMA_CTL_READ);
> + }
> + } else {
> + iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
> + while (pos-- > 0)
> + ioread8(fw_cfg_reg_data);
> + ioread8_rep(fw_cfg_reg_data, buf, count);
> + }
> +
> +end:
> mutex_unlock(&fw_cfg_dev_lock);
>
> acpi_release_global_lock(glk);
> +
> + return ret;
> }
>
> /* clean up fw_cfg device i/o */
> @@ -192,7 +314,7 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev)
> #endif
>
> /* verify fw_cfg device signature */
> - fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE);
> + fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE, false);
> if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
> fw_cfg_io_cleanup();
> return -ENODEV;
> @@ -201,9 +323,6 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev)
> return 0;
> }
>
> -/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
> -static u32 fw_cfg_rev;
> -
> static ssize_t fw_cfg_showrev(struct kobject *k, struct attribute *a, char *buf)
> {
> return sprintf(buf, "%u\n", fw_cfg_rev);
> @@ -351,8 +470,7 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
> if (count > entry->f.size - pos)
> count = entry->f.size - pos;
>
> - fw_cfg_read_blob(entry->f.select, buf, pos, count);
> - return count;
> + return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
> }
>
> static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> @@ -505,7 +623,7 @@ static int fw_cfg_register_dir_entries(void)
> struct fw_cfg_file *dir;
> size_t dir_size;
>
> - fw_cfg_read_blob(FW_CFG_FILE_DIR, &count, 0, sizeof(count));
> + fw_cfg_read_blob(FW_CFG_FILE_DIR, &count, 0, sizeof(count), false);
> count = be32_to_cpu(count);
> dir_size = count * sizeof(struct fw_cfg_file);
>
> @@ -513,7 +631,7 @@ static int fw_cfg_register_dir_entries(void)
> if (!dir)
> return -ENOMEM;
>
> - fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size);
> + fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size, true);
>
> for (i = 0; i < count; i++) {
> dir[i].size = be32_to_cpu(dir[i].size);
> @@ -544,9 +662,10 @@ static int fw_cfg_sysfs_probe(struct platform_device *pdev)
> * one fw_cfg device exist system-wide, so if one was already found
> * earlier, we might as well stop here.
> */
> - if (fw_cfg_sel_ko)
> + if (dev)
> return -EBUSY;
>
> + dev = &pdev->dev;
> /* create by_key and by_name subdirs of /sys/firmware/qemu_fw_cfg/ */
> err = -ENOMEM;
> fw_cfg_sel_ko = kobject_create_and_add("by_key", fw_cfg_top_ko);
> @@ -562,7 +681,7 @@ static int fw_cfg_sysfs_probe(struct platform_device *pdev)
> goto err_probe;
>
> /* get revision number, add matching top-level attribute */
> - fw_cfg_read_blob(FW_CFG_ID, &fw_cfg_rev, 0, sizeof(fw_cfg_rev));
> + fw_cfg_read_blob(FW_CFG_ID, &fw_cfg_rev, 0, sizeof(fw_cfg_rev), false);
> fw_cfg_rev = le32_to_cpu(fw_cfg_rev);
> err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
> if (err)
> @@ -587,6 +706,7 @@ static int fw_cfg_sysfs_probe(struct platform_device *pdev)
> err_name:
> fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
> err_sel:
> + dev = NULL;
> return err;
> }
>
> --
> 2.15.0.rc0.40.gaefcc5f6f
>

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